In the preparation of cefdinir, a cephalosporin antibiotic, deprotection reaction of the carboxy-protected cefdinir is usually conducted in a strongly acidic medium, e.g., trifluoroacetic acid (U.S. Pat. No. 4,559,334). Such a strong acid treatment step, however, generates undesired by-products including E-isomer (anti-form) of cefdinir; and, as a result, many methods have been developed to remove the contaminant E-isomer. For example, the method disclosed in International Publication No. WO98/45299 comprises converting crude cefdinir into a salt of dicyclohexylamine, removing the impurity and reconverting the purified salt to cefdinir. However, this multi-step method is inefficient and gives a low productivity.
U.S. Pat. No. 4,935,507 discloses a method of producing crystalline cefdinir, which comprises the steps of reacting amorphous cefdinir with an acid in a solvent and adding a non-polar solvent thereto to precipitate an acid-added salt of cefdinir, e.g., cefdinir.HCl, cefdinir.H2SO4 and cefdinir.CH3SO3H. However, the acid-added salt formed as an intermediate in this method is an amorphous bulky material which has poor stability and shows low purity.
Thus, there has continued to exist a need to develop an improved process for preparing a highly pure cefdinir.